This invention relates to a novel zirconium based alloy plate, a method of manufacturing the alloy plate, a fuel channel and a fuel assembly both using the alloy plate.
Zirconium alloy is a material having high corrosion resistance and a small neutron absorption cross section and is therefore used for a reactor fuel assembly member. For this kind of use, Zr--Sn--Fe--Cr--Ni alloys called zircaloy-2 and zircaloy-4 are mainly used. If these alloys are used in a nuclear reactor for a long period of time, elongation and bow deformation in particular directions occur because (0001) planes thereof are oriented in the direction of plate thickness. If the bow deformation occurs in a fuel channel box, the space for driving the control rod is reduced, which impedes the operation of the reactor. Furthermore, if the bow deformation occurs, the distance to the fuel cladding tube is changed with the result that the ratio of water to uranium is locally changed, thereby causing a change in fission reactivity. As a result, the corrosion of the fuel cladding tube is accelerated by abnormal heating, and further fuel damage may thereby be caused. To prevent the bow deformation of the fuel channel box from occurring due to such non-uniformity of neutron exposure, uniformization of neutron exposure by changing the fuel assembly loading position in the reactor core has been examined. This means, however, has not succeeded in preventing the bow deformation. The reduction in the control rod driving space and the change in fission reactivity both caused by the bow deformation are major factors of limitation of the service life of the fuel channel box.
As a method of preventing the bow of the fuel channel box, making orientation of crystal grain random is disclosed in JP-A-59-229475, JP-A-62-200286, JP-A-5-17837 and JP-A-5-80170. However, the bow deformation due to irradiation growth cannot be further reduced fully due to the reason described below.
The prior arts make crystal orientation of zirconium alloy members random. However, a channel box is quadrilateral and tubular, and, particularly, JP-A-5-17837 and JP-A-5-80170 disclose that, in order to make crystal orientation random, a heat treatment is performed by performing heating in a .beta. temperature range followed by quenching, however, it is difficult to heat and to keep the whole at uniform temperature. Consequently, if the whole member is not heated and kept at uniform temperature, there arises the difference in deformation by neutron irradiation, by which difference bowing occurs.